Kinase Subfamily MASTL

Kinase Classification: Group AGC: Family MAST: Subfamily MASTL

MASTL is an animal/fungal kinase that activates mitosis by inhibition of an inhibitory phosphatase.

Evolution

MASTL is found in fungi and animals, but is lost in nematodes. Members include MASTL in humans and gwl in Drosophila. The fungal form, RIM15 has a different domain structure and is not a definitive ortholog by sequence analysis, but has analogous functions.

Domain Structure

Animal MASTL consists just of a kinase domain that has a long atypical insert. Other AGC and MAST kinases have the AGC C-terminal tail domain. In MASTL this is truncated and degraded, and lacks the hydrophobic motif that is used by PDK1 to activate other AGC kinases, though it retains other motifs and is seen to wrap around the kinase domain [1].

Fungal RIM15 homologs have divergent kinase domains and are longer, including an N-terminal PAS domain and a C-terminal histidine kinase receiver domain.

Functions

MASTL controls entry into mitosis by phosphorylation of enosulfine (ensa in Drosophila, ENSA and ARPP-19 in human, igo1/2 in yeast). Endosulfine in turn binds and inhibits the PPA2/B55 phosphatase complex, which is an antagonist of the CDK1 mitotic kinase. Hence, MASTL function is required to drive mitosis, by inhibiting an inhibitor of CDK1. This has been shown in human, mouse, Xenopus, Drosophila and yeast (for review, see [2]).

MASTL kinase activity fluctuates through the cell cycle. CDK1 phosphorylates MASTL in a conserved region within the kinase insert (T194 and T207 in human), which allows autophosphorylation on the tail (S875 in human, equivalent to the turn motif in other AGC kinases) [3]. These sites are widely conserved in animals but not in fungi. Turn motif mutants were functional in mouse MEFs suggesting that this phosphorylation is not essential (Erguvin et al, 2021 bioarchiv).

In turn, both MASTL and endosulfine are substrates of PP2A/B55 as well as FCP1 phosphatase [4, 5]

PP2A and endosulfine are found in most eukaryotes [6, 7], but MASTL is restricted to animals and fungi. The MASTL phosphorylation site is conserved in all endosulfine, suggesting that other kinases may activate it in these other species. However, MASTL has been lost from C. elegans and mutation of the phosphorylation site in the endosulfine, ensa-1, does not appreciably alter cell division, suggesting that no other kinase controls this site in nematodes [8].

In yeast, RIM15 phosphorylation of endosuflines igo1/2 appears to activate rather than repress PP2A, which in yeast is a promoter rather than inhibitor of mitosis [9]. RIM15 is best known for transducing multiple nutrient sensors to drive either quiescence (G0) or meiosis, during nutrient limitation. In growth conditions, TORC1 is activated, which activates PKA, which phosphorylates RIM15. This causes it to bind 14-3-3 proteins and be sequestered in the cytoplasm. Nutrient stress inactivates TORC1 and PKA, leading to nuclear entry for RIM15, where is modulates G1 arrest or meiosis [10]. Some RIM15 is seen in the nucleus, where it may be inhibited by phosphorylation on the PAS domain by CDK8 kinase [11].

MASTL is associated with human cancers due to its role in regulating mitosis. MASTL protein is overexpression in a variety of colorectal tumors and cell lines [12]. Overexpression in immortalized MCF10A mammary gland cells, NIH 3T3 cells, or TERT-immortalized human primary fibroblasts drove transformation, while a kinase-dead form caused cell death [].

AKT phosphorylates MASTL at residue T299, which plays a critical role in its activation. Our results suggest that AKT increases CDK1-mediated phosphorylation and hence the activity of MASTL, which, in turn, promotes mitotic progression through PP2A inhibition. We also show that the oncogenic potential of AKT is augmented by MASTL activation, since AKT-mediated proliferation in colorectal cell lines can be attenuated by inhibiting and/or silencing MASTL. = Reshi, 32123010

Overexpression of human MASTL also drove phosphorylation and activation of Akt [12], via an indirect mechanism - MASTL promoted dephosphorylation and activation of GSK3, causing degradation of the PHLPP phosphatase, which reduced dephosphorylation of Akt on S473. This effect appeared to be independent of endosulfines, the only known MASTL substrates.

References

1. Ocasio CA, Rajasekaran MB, Walker S, Le Grand D, Spencer J, Pearl FM, Ward SE, Savic V, Pearl LH, Hochegger H, and Oliver AW. A first generation inhibitor of human Greatwall kinase, enabled by structural and functional characterisation of a minimal kinase domain construct. Oncotarget. 2016 Nov 1;7(44):71182-71197. DOI:10.18632/oncotarget.11511 |
2. Castro A and Lorca T. Greatwall kinase at a glance. J Cell Sci. 2018 Oct 24;131(20). DOI:10.1242/jcs.222364 |
3. Blake-Hodek KA, Williams BC, Zhao Y, Castilho PV, Chen W, Mao Y, Yamamoto TM, and Goldberg ML. Determinants for activation of the atypical AGC kinase Greatwall during M phase entry. Mol Cell Biol. 2012 Apr;32(8):1337-53. DOI:10.1128/MCB.06525-11 |
4. Della Monica R, Visconti R, Cervone N, Serpico AF, and Grieco D. Fcp1 phosphatase controls Greatwall kinase to promote PP2A-B55 activation and mitotic progression. Elife. 2015 Dec 14;4. DOI:10.7554/eLife.10399 |
5. Hégarat N, Vesely C, Vinod PK, Ocasio C, Peter N, Gannon J, Oliver AW, Novák B, and Hochegger H. PP2A/B55 and Fcp1 regulate Greatwall and Ensa dephosphorylation during mitotic exit. PLoS Genet. 2014 Jan;10(1):e1004004. DOI:10.1371/journal.pgen.1004004 |
6. Labandera AM, Vahab AR, Chaudhuri S, Kerk D, and Moorhead GB. The mitotic PP2A regulator ENSA/ARPP-19 is remarkably conserved across plants and most eukaryotes. Biochem Biophys Res Commun. 2015 Mar 20;458(4):739-44. DOI:10.1016/j.bbrc.2015.01.123 |
7. Chen MJ, Dixon JE, and Manning G. Genomics and evolution of protein phosphatases. Sci Signal. 2017 Apr 11;10(474). DOI:10.1126/scisignal.aag1796 |
8. Kim MY, Bucciarelli E, Morton DG, Williams BC, Blake-Hodek K, Pellacani C, Von Stetina JR, Hu X, Somma MP, Drummond-Barbosa D, and Goldberg ML. Bypassing the Greatwall-Endosulfine pathway: plasticity of a pivotal cell-cycle regulatory module in Drosophila melanogaster and Caenorhabditis elegans. Genetics. 2012 Aug;191(4):1181-97. DOI:10.1534/genetics.112.140574 |
9. Juanes MA, Khoueiry R, Kupka T, Castro A, Mudrak I, Ogris E, Lorca T, and Piatti S. Budding yeast greatwall and endosulfines control activity and spatial regulation of PP2A(Cdc55) for timely mitotic progression. PLoS Genet. 2013;9(7):e1003575. DOI:10.1371/journal.pgen.1003575 |
10. Sarkar S, Dalgaard JZ, Millar JB, and Arumugam P. The Rim15-endosulfine-PP2ACdc55 signalling module regulates entry into gametogenesis and quiescence via distinct mechanisms in budding yeast. PLoS Genet. 2014 Jun;10(6):e1004456. DOI:10.1371/journal.pgen.1004456 |
11. Willis SD, Hanley SE, Doyle SJ, Beluch K, Strich R, and Cooper KF. Cyclin C-Cdk8 Kinase Phosphorylation of Rim15 Prevents the Aberrant Activation of Stress Response Genes. Front Cell Dev Biol. 2022;10:867257. DOI:10.3389/fcell.2022.867257 |
12. Vera J, Lartigue L, Vigneron S, Gadea G, Gire V, Del Rio M, Soubeyran I, Chibon F, Lorca T, and Castro A. Greatwall promotes cell transformation by hyperactivating AKT in human malignancies. Elife. 2015 Nov 27;4. DOI:10.7554/eLife.10115 |